The present invention relates to video cameras and, more particularly, to color video cameras having automatic or semi-automatic white balance control systems.
Video cameras are known in which automatic or semi-automatic white balance control circuits are supplied. In the fully automatic systems, the variation in color temperature of the illumination is measured by a photo sensor such as a photo diode. The output of the photo diode is signal processed and used in an electronic circuit to control the RB gains, thereby to obtain the white balance.
In the semi-automatic systems, the criterion for white balance is that the color-difference signal is 0 when a white object is shot. The camera is first directed to a white object and at the same time an automatic white control switch is depressed. Thereupon a color control is effected by the electronic circuit such that the color-difference signals become 0. After the above adjustment, the circuit conditions are maintained. When the shooting conditions have changed, it is necessary to depress the automatic white control switch again to obtain a proper adjustment.
The above circuits are state of the art. Their exact operation is not a part of the present invention and only as much of it as is necessary to explain the operation of the present invention will be described.